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Food deserts? Healthy food access in Amsterdam

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1. Introduction Overweight and obesity have become pandemic and are considered global health challenges (Ng et al., 2014): 1.9 billion adults are now overweight, and 600 million of these adults are obese (WHO, 2015). These ﬁgures have doubled since the 1980s. The Netherlands is no exception to this trend: The proportion of overweight people increased between 1981 and 2013 from 22.9% to 31.5% (CBS, 2015), and that of obese people from 4.4% to 10.1%. This is alarming, because both overweight and obesity are closely associated with non-communicable diseases (e.g., diabetes, musculoskeletal disorders, and cardiovascular diseases) (Rubenstein, 2005). Although the causes are complex and multifactorial, there are two major viewpoints concerning the epidemic pathway to overweight and obesity (Ball, Timperio, & Crawford, 2006). First,

individuals are responsible for their own weight gain, food intake, and energy consumption. Second, it is assumed that external factors such as an obesogenic food environment1 affect people's consumption behavior and diet (Ball et al., 2006; Glanz, Sallis, Saelens, & Frank, 2005). From the latter perspective, overweight and obesity are a normal response to an abnormal environment. Empirical results for the association between the physical food environment e here deﬁned as the accessibility/availability of places that sell healthy food (i.e., supermarkets) in the local environment e and individual dietary intake or weight status are inconsistent (Black, Moon, & Baird, 2014; Caspi, Sorensen, Subramanian, & Kawachi, 2012; Cobb et al., 2015). Reviews (Beaulac, Kristjansson, & Cummins, 2009; Hilmers, Hilmers, & Dave, 2012) suggest that limited access to healthy food partially explains dietary inequalities across urban neighborhoods. Findings show that people living in neighborhoods with low socioeconomic status and those living in ethnic minority neighborhoods are more prone to unhealthy diets, compared to those living in high

1 Food environments refer to “the sum of inﬂuences that the surroundings, opportunities, or conditions of life have on promoting obesity in individuals or populations” (Swinburn, Egger, & Raza, 1999, p. 564).

groups that have similar accessibility and neighborhood characteristics (Hagenauer & Helbich, 2013a). Taken together, while empirical evidence for food deserts in U.S. urban landscapes is extensive (Beaulac et al., 2009; Taylor & Ard, 2015; Walker et al., 2011), ﬁndings for Canada are mixed (Larsen & Gilliland, 2008; Lu & Qiu, 2015; Smoyer-Tomic, Spence, & Amrhein, 2006). For example, Apparicio et al. (2007) and Gould, Apparicio, and Cloutier (2012) found that socioeconomically deprived neighborhoods have in fact better access to affordable and healthy food, while Larsen and Gilliland (2008) found the opposite for Montreal. Others, including Cushon et al. (2013) and SmoyerTomic et al. (2006), did not conﬁrm an accessibilityesocioeconomic association. Cultural, economic, and regulatory differences or the provision of affordable and wholesome food make it difﬁcult to transfer results from North America to Europe (Cummins & Macintyre, 2006). Shaw (2012), for instance, identiﬁed some areas in Nantes, France, that have both poor access to food outlets and low socioeconomic proﬁles. For the UK, Clarke, Eyre, and Guy (2002) found food deserts in Leeds/Bradford and Cardiff in neighborhoods with low socioeconomic status; in contrast, Macdonald, Ellaway, and Ball (2011) concluded that no population groups are signiﬁcantly disadvantaged in British cities as a result of the spread a k and densiﬁcation of food outlets. Kriẑan, Bilkov a, Kita, and Horn (2015) conﬁrmed these ﬁndings of satisfactory access to healthy food across the residents of Bratislava, Slovakia. Even though these studies contributed signiﬁcantly to our understanding of food deserts, several shortcomings remain. First, although there is compelling evidence for food deserts in North American cities (e.g., Apparicio et al., 2007; Larsen & Gilliland, 2008), investigations for continental Europe are scarce (e.g., Kriẑan et al., 2015; Shaw, 2012). Yet, to date, there is no research for the Netherlands. This is surprising for cities such as Amsterdam, where signiﬁcant health disparities across neighborhoods are documented (GGD Amsterdam, 2013). Second, from a methodological point of view, studies largely remain at a coarse analytical level (e.g., census tracts) (e.g., Clarke et al., 2002; Cushon et al., 2013; Smoyer-Tomic et al., 2006). Inconsistencies in empirical ﬁndings might be caused by the way that geographic boundaries for neighborhood deﬁnitions are chosen (Barnes et al., 2016), whereas scale and zoning effects can be signiﬁcantly reduced by employing at least aggregated data (Openshaw, 1984). Thus, local variations in food accessibility within a spatial unit call for microgeographic analyses at a grid level. Third, with few exceptions (e.g., Apparicio et al., 2007), food deserts are rarely identiﬁed based on multivariate cluster analyses that group data objectively and coherently. Fourth, the review by Lamb et al. (2015) emphasized methodological ﬂaws in most food desert studies (Wang et al., 2016). The fact that adjacent spatial units share similar attributes (i.e., are spatially dependent) is usually ignored, even though this has serious consequences for non-spatial statistical analysis, including clustering (Hagenauer & Helbich, 2013a). This calls the validity of the ﬁndings partially into question. This research addressed the aforementioned shortcomings and was the ﬁrst to investigate the associations between, on the one hand, the accessibility of supermarkets and, on the other hand, property prices and the share of native Dutch people (i.e., persons whose parents were born in the Netherlands) in Amsterdam, on a spatial micro-scale with a spatial resolution of 100 meters. Specifically, while also utilizing multivariate statistics, we used an innovative and spatially explicit clustering approach, namely contextual neural gas (CNG). An understanding of local food environments is an important ﬁrst step toward combatting the increasing prevalence of population overweight and obesity (Ng et al., 2014). Our ﬁndings are essential for decision-makers to promote food equity and to formulate policies toward healthy food environments.

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2. Study area and data 2.1. Study area Amsterdam is the Netherlands' largest municipality (825,080 residents) (CBS, 2015). It was chosen for three reasons. First, approximately 40 percent of the residents are overweight, and 75 percent of the adults do not consume the recommended amount of fruit and vegetables (GGD Amsterdam, 2013). Second, the residents do not experience health problems equally. For instance, the health monitor reports that the prevalence of overweight and obesity differs signiﬁcantly between ethnicities (e.g., Moroccan 60% vs. 35% Dutch). Third, there are distinct differences in overweight and obesity across space, with a higher prevalence in the central areas (22%) and a sharp increase toward the northern districts (34%) (GGD Amsterdam, 2013). These health inequalities are assumed to be translated into local food environments, which made Amsterdam ideal for this investigation. 2.2. Datasets Following the majority of studies (e.g., Barnes et al., 2016; Kriẑan et al., 2015; Larsen & Gilliland, 2008), we used supermarkets as food vendors offering a wide variety of healthy food. Supermarkets were deﬁned as the standard grocery stores of the major chains operating in the Netherlands (e.g., Albert Heijn, Jumbo). Chain supermarkets have higher price competitiveness than small grocery shops (Zenk et al., 2005). Although organic supermarkets and farmers' markets provide healthy food (Lu & Qiu, 2015; Wang et al.,

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2014), their pricing is less competitive (Zenk et al., 2005). We thus excluded them from our analyses. “To go” stores were disregarded as they offer ready-to-eat products and are mainly located at places with high levels of commuter trafﬁc. The location of each supermarket was collected through the website of each chain. To avoid boundary effects (Van Meter et al., 2010), stores within a buffer zone of two kilometers around Amsterdam were taken into account. Of the 144 supermarkets considered, 122 are located within the administrative area. The store addresses were geocoded with the Dutch cadastral data “Basisregistraties Adressen en Gebouwen.” Fig. 1 shows the distribution of the supermarket locations. To circumvent aggregation bias, scale, and zoning effects related to administrative areas (Barnes et al., 2016), this research conceptually followed Shaw (2012) in terms of using a grid representation but utilizing a more detailed spatial resolution of 100 meters. The grid was superimposed over the study area. Cells without any residents were excluded, resulting in N ¼ 5242 cells. While Statistics Netherlands still provides socioeconomic data, such a microscale is already close to address-based analyses. Area-level socioeconomic characteristics were represented by a proxy variable reﬂecting the average value (in V1000) of all properties registered as residential (HOUS) within a cell for the years 2011 and 2012 (i.e., the higher the property prices, the higher the status; Fig. 2) (Braveman et al., 2005). Since neighborhood ethnicity was repeatedly associated with food deserts (Walker et al., 2011), the share of native Dutch people (NATI) within a cell for the year 2014 was also considered (Fig. 3). Both variables were available at an ordinal level.

Fig. 1. Study area and the supermarket locations (in brackets: the total number of locations per supermarket chain within the buffered Amsterdam area; base map provided by ESRI).

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Fig. 2. Average property value per cell (in V1000).

3. Methods 3.1. Accessibility measures Following Apparicio et al. (2007), Cushon et al. (2013), and Gould et al. (2012), the research design utilized the following three accessibility measures computed for each cell in a GIS using ESRI street data for the year 2008: 1) Proximity (PROX): This measure reﬂects the street network distance in meters from each cell centroid i to the closest supermarket j of any chain. 2) Density (DENS): This indicator represents the number of supermarkets j within a street network buffer around each centroid i. The threshold distance of 1000 meters (approximately a 12-minute walk for an adult in a city) was used, following previous studies (Charreire et al., 2010). 3) Variety (VARI): This measure represents residents' variety of choice in terms of both food products and prices, since not all supermarket chains offer the same goods at the same price (Drewnowski et al., 2014). Variety represents the mean street network distance from each centroid i to the three nearest supermarkets j from k different chains.

3.2. Statistical analyses Key descriptive statistics were determined not only for each variable, but also for two stratiﬁcations representing

neighborhoods with high/low property prices and a high/low share of native Dutch people, as in Lu and Qiu (2015). The threshold values were set through the lowest quartile of the property prices (V176,000). A neighborhood dominated by ethnic minorities was represented by a share of native Dutch people